1. Field of the Invention
The present invention relates to soundproofing covers and methods of manufacturing the soundproofing covers. More particularly, the present invention relates to an improvement of a soundproofing cover including a cover body and a sound absorbing layer made of a urethane foam and formed integrally with a back surface of the cover body, and a method of advantageously manufacturing the soundproofing cover.
2. Description of the Related Art
Soundproofing covers have been attached to various types of noise sources to prevent leakage of noise to the outside. For example, a soundproofing cover may be attached to a cylinder head cover of a vehicle engine to prevent leakage of noise generated in the engine.
Soundproofing covers having various structures are known. An example of such a soundproofing cover includes a cover body formed of a hard resin-molded article and a sound absorbing layer made of a urethane foam and fixed to a back surface of the cover body (see, for example, Japanese Unexamined Patent Application Publication No. 2003-50585). The soundproofing cover including the sound absorbing layer is preferably manufactured by the following method. That is, first, a cover body that has been separately formed is placed in a mold cavity of a mold, and a part of the mold cavity at the back side of the cover body is filled with a urethane resin composition. Then, the urethane resin composition is foamed, so that the sound absorbing layer made of the urethane foam is formed integrally with the back surface of the cover body. In this case, the design freedom for the shape of the sound absorbing layer can be advantageously increased.
In general, various components, members, etc. to be fixed to the vehicle engine are arranged around the soundproofing cover or the like that is attached to the cylinder head cover of the engine. These components and members are generally attached to the cylinder head cover with brackets or the like. More specifically, many known cylinder head covers have cylindrical boss portions that are formed integrally therewith. The boss portions are arranged so as to extend through holes formed in the soundproofing cover and project upward from the soundproofing cover. The brackets to which the components and members arranged above the soundproofing cover are fixed are attached to the cylinder head cover by screwing bolts into the boss portions.
However, because the soundproofing cover has through holes for allowing the boss portions to extend therethrough, noise leaks through the gaps between the inner peripheral surfaces of the through holes and the outer peripheral surfaces of the boss portions. Therefore, the soundproofing cover with the through holes according to the related art has a problem that the soundproofing performance is reduced owing to the noise leakage through the through holes.
The noise leakage through the through holes in the soundproofing cover may be prevented by eliminating the through holes by embedding nut members used to fasten the brackets or the like with screws or bolts in the cover body of the soundproofing cover. The nut members are embedded in a manner such that bearing surfaces thereof are exposed at the front surface of the cover body, that is, such that threaded holes open in the front surface of the cover body.
However, when the soundproofing cover is manufactured by the above-described preferred method in which the sound absorbing layer made of the urethane foam is formed integrally with the back surface of the cover body by foaming the urethane resin composition in the mold in which the cover body is placed, embedding the nut members in the soundproofing cover may cause the following problems.
That is, for economic reasons, nut members having threaded holes that are open at both sides of the nut members in the axial direction are generally used as the nut members to be embedded in the cover body of the soundproofing cover. Therefore, when the cover body in which the nut members are embedded is placed in the mold cavity and the urethane resin composition is foamed, there is a risk that the urethane resin composition that flows in the mold cavity will enter the threaded holes in the nut members through the openings at the side opposite to the bearing surfaces. If this happens, the urethane resin composition solidifies in the threaded holes and it becomes difficult to fasten the screws, bolts, or the like to the nut members, owing to the solidified urethane foam.